highly unlikely for them to reproduce in a non-dedicated breeding system.
I know everyone's experiences are different but, from my experience, I would disagree with this. However, my experience with ghosties is only in a freshwater system, at the moment.
I have had ghost shrimp reproduce in my fw tank, with a very predatory angel fish constantly scouring the tank for them (and some other species that would take the occasional nip at them). The trick is to provide them with enough hiding spots so they can evade predators. Also, don't overstock your tank with too many predators.
Again, my experience relates to a freshwater set-up. It might be very different with regards to a saltwater set-up. But, I did buy ghosties already in berry (with eggs) and observed them producing several more clutches over time. I also noticed, over time, several apparently new, and smaller, shrimp in the tank as time went by....smaller than the original shrimp that were purchased. So, it is possible, and maybe better than "highly" unlikely that they would reproduce in certain set-ups, providing predation pressure is low. Obviously, if you have lots of large fish or very active night-feeders, they'll never really get a chance to breed.
That being said, I do agree that they would do much better in a dedicated system. I plan on putting them in my sump and letting them go to town. Their offspring should get sucked up into the return and help supplement the main tank.